The present invention relates to a positioning apparatus for use with a semiconductor exposure system to be used for forming a pattern on a flat substrate, such as a semiconductor wafer or a liquid-crystal panel, as well as with an assembly/inspection apparatus and a precision machine tool.
[Patent Document 1] JP-A-2002-158274
A positioning apparatus described in, e.g., JP-A-2002-158274, is the positioning apparatus of this type. This patent publication discloses a positioning apparatus intended for providing a high-precision, long-life positioning apparatus which can actuate a slider at high speed and has achieved space saving. The positioning apparatus has a first positioning device for positioning a first slider (an intermediate stage) to a base in an X-axis direction by means of a first drive device; and a second positioning device for positioning a second slider (the intermediate stage) on the base in a Y-axis direction by means of a second drive device. The first and second drive devices are provided on the base, and the first and second sliders are arranged so as to overlap in a Z-axis direction. A stage is engaged with both the first and second sliders.
The stage of the positioning apparatus is characterized in that a fine movement shaft, a workpiece chuck, or a transfer mechanism, which are to be mounted on the stage, are arranged on a base-side of the stage (i.e., a lower side of the stage in the Z-axis direction) by way of a hole formed in the center of the stage. In order to prevent interference with these elements mounted on the stage, the through hole is formed in the respective intermediate stages. A drive element, such as a ball screw, and a guide element, such as a linear guide, are provided on an edge section of the intermediate stage instead of at the center thereof.
Since the through holes are formed in the above-described intermediate stages, there arises a problem of the intermediate stages having low stiffness; especially, insufficient stiffness in a yawing direction. In the meantime, the intermediate stages are supported by guide rails laid on the base, thereby enhancing the yawing stiffness of comparatively-intermediate stages. The hollow structure of the intermediate stages has originally suffered a problem of low horizontal stiffness of the entire intermediate stages, because the hollow structure deteriorates the stiffness of the intermediate stages acting as sheet materials. The problem is described more specifically as follows.
FIG. 2 is a schematic view showing the layout of linear guide rails 60A, 60B and a ball screw shaft 52 with respect to an intermediate stage 12. The intermediate stage 12 is movably supported on the linear guides and the ball screw shaft 52, by means of linear guide bearings (31A, 31B, 31E, and 31F) and a ball screw nut 52D.
In such a construction, the ball screw shaft 52 is disposed at a brim of the intermediate stage. Hence, the rotational center of the stage is located around the ball screw nut. The linear guides (constituted of the linear guide rail 60B and the linear guide bearings 31A, 31B) located close to the ball screw possess the force of constraint (i.e., the force of resistance to a screw) against vibrations in the yawing direction of the stage (i.e., the direction designated by the arrow in FIG. 2).
The stiffness of the intermediate stage 12 is low in an area thereof located opposite the area where the ball screw shaft 52 is located. For this reason, in response to vibrations in the intermediate stage 12 in the yawing direction, the linear guide bearings 31E, 31F constituting the linear guide in the opposite area are vibrated in an advancing direction. This is attributable to a low-stiffness portion (i.e., a hollow section) 24 (100) of the intermediate stage 12 becoming elastically deformed before the linear guide—which is located in the area opposite the area where the ball screw shaft is located—exhibits the original force of resistance against the vibrations arising in the yawing direction.
Specifically, the previously-described positioning apparatus has a hollow shape, and therefore the linear guide located in the area opposite the ball screw shaft 52 fails to exhibit stiffness in the yawing direction. Therefore, there is a drawback of the stiffness of the intermediate stages in the yawing direction being low. Hence, there is a problem of the inability to accurately position the stage.